The present invention relates to a printing apparatus having a printing unit and a paper sheet supply unit for supplying printing paper to the printing unit.
Such printing apparatus as serial printer, dot printer or thermal printer which has such printing unit and paper sheet supply unit has been known. The printing unit includes a carriage comprising a printing head for printing the paper sheet supported around a platen and a paper guide disposed in facing relation to the platen for guiding the paper and a driving unit for driving the carriage in a longitudinal direction of the platen. The paper sheet supply unit is mounted on the printing unit integrally or detachably.
In the printing apparatus of this type, it has been proposed to provide a guide member for paper discharge in the paper sheet supply unit so that a carrying direction of paper after having passed through the printing unit is defined precisely. With such guide means, it is possible to guide the paper after being printed in a predetermined direction, so that the paper sheet guiding becomes improved.
In a proposed construction, a paper supplied manually or automatically by the paper sheet supply unit is set in a predetermined position by sensing the paper to the guide member while a front edge of the paper is guided by the paper guide provided on the carriage. Since in the conventional printing apparatus, there is no printing operation during a supplying and setting of the paper, the carriage is returned to a home position in one end of the platen. Therefore, a portion of the front edge of the paper which passes through a region in the vicinity of the carriage is guided by the paper guide of the carriage and sent to the guide member. However, another portion of the front edge of the paper which is remote from the carriage cannot be fully guided by the paper guide and impinges with the guide member, resulting in a trouble. This is particularly true when the paper sheet is wide or thick.
On the other hand, a direction in which the front portion of the paper sheet after passed through a printing region moves depends upon the stiffness and size of the paper and an operating direction of a printing component of the printing head, e.g. a hammer, with respect to the paper, etc. In order to reliably guide the front edge portion of the paper regardless of the moving direction of the paper, it is necessary to enlarge the width of the guide member to thereby enlarge a paper receiving area thereof so that the front edge portion of the paper is always received by the guide member necessarily. However, when the guide member is enlarged, it becomes an obstacle in exchanging components of the printer which are mounted exchangeably. For example, a ribbon cartridge containing a printing ribbon is usually mounted on the printing head exchangeably. When the guide member is so enlarged, the ribbon cartridge is hardly detached or mounted without removing it or the automatic paper supply means.